Evaluation of phenol diffusivity through Pseudomonas putida biofilms: Application to the study of mass velocity distribution in a biofilter

Phenol diffusivity through Pseudomonas putida biofilms with thickness ranging from about 9 . 10(-6) to 90 . 10(-6) m has been evaluated in order to carry out a kinetic study on phenol aerobic degradation in a biofilter. An average effective diffusivity of 8.92.10(-12) m(2) s(-1) has been calculated at 20 degrees C, with no appreciable dependence on biofilm thickness. This value, that is only 0.6% of that calculated in water at the same temperature, has been used to carry out a comparison between diffusion, convection and bioreaction mass velocities along the biofilter fed with air streams contaminated with different levels of phenol. Although diffusion through the biofilm is the limiting step at local level, biomass grows so abundantly within the support pores at high residence time that the most superficial active layers of biofilm are enough to transform nearly completely the substrate fed. At low residence time, on the contrary, the system is not able to face an evident situation of substrate overloading. Deodorization tests have also been carried out varying the support porosity, the superficial gas flow rate, and the starting phenol concentration in the polluted gaseous stream. This study could provide a general tool to model fixed-bed columns.